1. Field of the Invention
The present invention relates to a laser apparatus and a laser machining apparatus of an intracavity wavelength conversion type, which converts a wavelength by placing a wavelength conversion crystal in a resonator.
2. Discussion of Background
FIG. 14 is a structural view of a conventional laser apparatus disclosed in JP-A-8-250797. In FIG. 14, numerical reference 25 designates a resonator mirror having a high reflectance with respect to a fundamental laser beam. Numerical references 2c, 2d designate solid-state laser active mediums. Numerical reference 9a designates a 90 degree polarization rotator. Numerical reference 4b designates a second harmonic generation wavelength conversion crystal. Numerical reference 6b designates a fundamental laser beam. Numerical reference 5b designates a laser optical axis of the fundamental laser beam. Numerical reference 3b designates a folding and outcoupling mirror having a high reflectance with respect to the fundamental laser beam and high transmittance with respect to the second harmonic laser beam. Numerical reference 26 designates a resonator mirror having a high reflectance with respect to the fundamental beam and second harmonic laser beam. The second harmonic generation wavelength conversion crystal 4b is provided with an optimum phase matching means by changing an angle and temperature of the frequency conversion crystal.
In the laser apparatus shown in FIG. 14, a part of the fundamental laser beam, which is generated by the mirrors 25, 26, the 90 degree polarization rotator 9a, and the solid-state laser active mediums 2c, 2d, is converted into a second harmonic laser beam by the second harmonic generation wavelength conversion crystal 4b placed inside of a resonator and extracted from a laser beam folding mirror 3b. In this laser apparatus, one of the resonator mirrors configurating the resonator is a convex mirror, and the other mirror 26 on a side close to the second harmonic generating wavelength conversion crystal 4b is a concave mirror. The second harmonic generation wavelength conversion crystal 4b is positioned where the diameter of the fundamental wave laser beam 6b is narrowed by a function of the resonator.
In the laser apparatus shown in FIG. 14, as the 90 degree polarization rotator 9a is positioned between the laser active mediums 2c, 2d, it is possible to improve stability and efficiency of a laser system by compensating the birefringence and the bifocusing of the two laser active mediums.
FIG. 15 is a structural view showing a laser apparatus disclosed in xe2x80x9cSolid State Laser Engineeringxe2x80x9d (3rd Edition) by W. Koechner. In FIG. 15, numerical reference 25a designates a resonator mirror having a concave curvature. Numerical reference 8b designates a resonator Q switching element. Numerical reference 2e designates a laser active medium. Numerical reference 5c designates a laser optical axis of a fundamental wave laser beam. Numerical reference 3c designates a folding and outcoupling mirror, which has a high reflectance with respect to the fundamental wave laser beam and a high transmittance with respect to second harmonic laser beam. Numerical reference 4c designates a second harmonic generation wavelength conversion crystal. Numerical reference 26a designates a mirror having a concave curvature, the mirror has a high reflectance with respect to the fundamental wave-laser beam and the second harmonic laser beam. In this apparatus, the second harmonic generation wavelength conversion crystal 4c is positioned at where the fundamental laser beam is narrowed by a function of the laser resonator like the apparatus illustrated in FIG. 14.
In a second harmonic laser beam generation apparatus constructed as in FIG. 15, a part of a fundamental Q pulse laser beam, which is generated by the resonator mirrors 25a, 26a, the reflective mirror 3c, the laser active medium 2e, and the Q-switching element 8b, is converted into second harmonic laser beam by the second harmonic generation wavelength conversion crystal 4c and extracted from the mirror 3c. 
In the laser systems, illustrated in FIGS. 14 and 15, the wavelength conversion crystal is positioned at where the laser beam diameter is narrowed in the vicinity of the concave mirror. As the wavelength conversion efficiency of the wavelength conversion crystal becomes high as the beam intensity increases, the wavelength conversion crystal is generally placed at where the laser beam is focused. A concave mirror is ordinarily used as the resonator mirror.
In thus constructed second harmonic laser beam generation apparatus, since the concave mirror is used as the resonator mirror, on at least a side in which the wavelength conversion crystal is positioned, the length of the resonator is increased, whereby a compact wavelength conversion laser apparatus could not be fabricated. Further, the resonator has low stability with respect to a vibration of the resonant mirror. Further, it is difficult to generate a wavelength conversion pulse laser beam with a narrow pulse width. In addition, when one tries to improve the output power and the efficiency of the system, wavelength conversion crystal is apt to be damaged. Meanwhile, in case that a wavelength conversion crystal having a small nonlinear constant is used, it is difficult to obtain high frequency conversion efficiency.
It is an object of the present invention to solve the above-mentioned problems inherent in the conventional laser apparatus and to provide an intracavity wavelength conversion laser apparatus, in which the pulse width is short; operation is easy; reproducibility and stability are excellent; a wavelength conversion crystal is less susceptible to damages; and the size is compact.
Another object of the present invention is to provide a wavelength conversion laser apparatus, which demonstrates high efficiency even in case when a wavelength conversion crystal has a small wavelength conversion coefficient.
Another object of the present invention is to provide a laser machining apparatus, which is easily and stably operated. And it is possible to process finely with high accuracy at high speed.
Another object of the present invention is to provide a laser apparatus, which is easily operated and could excite another laser system, stably and efficiently.
According to a first aspect of the present invention, there is provided a laser apparatus having a stable resonator and a mirror, wherein the stable resonator includes a solid-state laser active medium, a Q factor modulating element, and a wavelength conversion crystal, and the convex mirror positioned on a side in the vicinity of the wavelength conversion crystal.
According to a second aspect of the present invention, there is provided the laser apparatus according to the first aspect of the invention, wherein the wavelength conversion crystal for generating a second harmonic laser beam is a type II phase matching type LBO (LiB3O5) crystal.
According to a third aspect of the present invention, there is provided the laser apparatus according to the first and second aspects of the invention, wherein at least one polarization controlling element is inserted inside of the resonator.
According to a fourth aspect of the present invention, there is provided the laser apparatus according to the first through third aspects of the invention, wherein an output power of a wavelength converted Q pulse laser beam is 50W or more.
According to a fifth aspect of the present invention, there is provided a laser machining apparatus, wherein the wavelength converted laser beam, generated from the laser apparatuses, according to the first through fourth aspects of the invention is used for processing.
According to a sixth aspect of the present invention, there is provided the laser apparatus according to the first through fourth aspects of the invention, wherein the wavelength converted laser beam, generated from the above laser apparatuses, is used as a beam source for extracavity wavelength conversion, by which the wavelength is converted by inserting a wavelength conversion crystal along optic axis of the wavelength converted laser beam.
According to a seventh aspect of the present invention, there is provided the laser apparatus according to the first through fourth aspects of the invention, wherein the laser beam having the converted wavelength, generated from the laser apparatuses, is used for exciting other laser""s active mediums.